A mini-excavator (i.e., hydraulic excavator whose operating mass is less than 6 tons) as an example of the construction machine generally comprises a lower travel structure, an upper rotating structure which is mounted on the lower travel structure to be rotatable, and a multijoint work implement (having a boom, an arm and a bucket) which is mounted on the upper rotating structure to be elevatable. The mini-excavator is equipped with, for example, a hydraulic pump, a plurality of hydraulic actuators (e.g., a boom hydraulic cylinder, an arm hydraulic cylinder, a bucket hydraulic cylinder, etc.), a plurality of directional control valves for respectively controlling the flow of the hydraulic fluid from the hydraulic pump to the hydraulic actuators, and operating means for controlling the directional control valves (specifically, a plurality of operating devices each of which outputs pilot pressure corresponding to the operating position of a control lever, for example).
In recent years, electric mini-excavators, employing an electric motor (motor/generator) instead of the engine as the driving source for the aforementioned hydraulic pump, are being proposed (see Patent Literature 1, for example) in consideration of their advantages of not emitting the exhaust gas and also reducing the noise and vibration significantly.